OK - I posted that process above. Let me post it again below.
What I am going to RECOMMEND is that you:
1) Stop the program - on the computer.
2) "Eject" the device from the computer - if it still shows as connection.
3) Physically removed the device from the computer (USB cable).
4) TEST if the device will still power up.
5) Shutdown and reboot computer.
6) Reconnect the device (assuming it DOES power up) - and TEST if the device is "seen" by the computer.
7) Restart Garmin Express and restart the update - making sure that NOTHING else is running on the computer - especially things that use a LOT of bandwidth (videos, music, etc.).